Why does a Tesla, even with its outer shell removed and only the chassis remaining, still resemble a work of art, and still have enough space in the front and rear to accommodate two large luggage compartments? A widely circulated explanation is this: "Tesla has strong integration capabilities; they use wheel-side motors."
The previous answer seemed to make some sense. However, it contained a rather serious error. Does placing Tesla's electric drive system between the two rear wheels automatically make it a wheel-side motor? Today, we'll discuss what wheel-side motors, hub motors, and centralized motors are to address this misconception.
Hub motor
In-wheel motor technology, also known as wheel-mounted motor technology, allows for independent drive of each wheel. Therefore, it can easily achieve front-wheel drive, rear-wheel drive, and four-wheel drive configurations, making full-time four-wheel drive very easy to implement in in-wheel motor-driven vehicles. Furthermore, in-wheel motors can achieve differential steering similar to tracked vehicles by varying the speeds of the left and right wheels, or even reversing their rotation, significantly reducing the vehicle's turning radius. In special circumstances, it can almost achieve turning on the spot, a capability highly valuable for special vehicles. Therefore, this technology is widely used in special vehicles such as mining trucks and engineering vehicles.
Michelin wheel hub motor structure
Furthermore, using in-wheel motors can greatly simplify the vehicle's structure, eliminating the need for traditional clutches, gearboxes, and driveshafts. This also means saving more space. More importantly, in-wheel motors can be used in parallel with traditional powertrains, which is equally significant for hybrid vehicles.
However, no mass-produced passenger vehicles on the market use this technology. After all these advantages, why don't mass-produced cars use it? The reason is that some of its drawbacks make it somewhat unsuitable for use in passenger vehicles. The hub motor needs to be installed inside the wheel rim, which increases the unsprung mass of the vehicle, making handling difficult. Secondly, the electric eddy current braking capacity is not high, and it needs to work in conjunction with a mechanical braking system in heavy vehicles.
For electric vehicles, achieving higher braking performance requires more energy, which affects driving range to some extent. Thirdly, even slight differences in power output can amplify the impact on vehicle steering control at high speeds, leading to loss of control. Furthermore, difficulty in lubrication causes faster wear and shorter lifespan of the planetary gear reduction mechanism, hinders heat dissipation, and results in higher noise levels due to poor manufacturing processes. High current is required during high-torque conditions such as starting, headwinds, or climbing hills, which can easily damage the battery and permanent magnets. The motor's peak efficiency range is small, and efficiency drops rapidly once the load current exceeds a certain value.
In conclusion, the integration of in-wheel motors with mass-produced passenger vehicles remains a story of mixed joy and sorrow.
Wheel-side motor
A wheel-side motor is a motor mounted on the side of the wheel to drive that wheel independently, while a hub motor is a motor embedded in the wheel wheel, with the stator fixed to the tire and the rotor fixed to the axle, rather than transmitting power to the wheel through a drive shaft.
Wheel-side motor drives typically come in two forms: hub motors and wheel-side motors in a narrower sense. What is a wheel-side motor in a narrower sense? A wheel-side motor refers to a drive where each drive wheel is driven by a separate electric motor, but the motor is not integrated into the wheel; instead, it is connected to the wheel via a transmission device (such as a drive shaft) (this is the difference between a hub motor and a wheel-side motor).
However, the electric motor installed on the vehicle body has a significant impact on the overall vehicle layout, especially in the case of rear-axle drive. Due to the considerable deformation and movement between the body and wheels, there are also certain limitations on the universal joint transmission of the drive shaft. Another point that I can't help but worry about is that if I had such a car, I'd probably be sleeping worrying that the wheels and motor would be stolen along with it.
Centralized electric motor
Currently, most well-known new energy vehicles, such as Tesla, BAIC New Energy, BYD's pure electric series, and JAC iEV series, use a centralized electric motor. However, with the development of electric and hybrid vehicles, more and more cars may be equipped with more than one centralized electric motor. In this case, one centralized electric motor may only transmit power to the front wheels, while the other centralized electric motor "works hard" on the rear wheels (for example, Tesla's various D series).
So here's the question: how can we understand this more intuitively? If someone asks you about the difference between the two, you can answer them like this: "A single motor placed in the center and simultaneously driving both wheels is called a centralized motor. Tesla is definitely not a wheel-side motor."
Summary | Advantages of wheel-side motor/hub motor drives over centralized motor drives:
① It uses electronic differential control technology to achieve different speeds for the inner and outer wheels when turning, and is suitable for special vehicles.
② Eliminating the mechanical differential device helps reduce the weight of the power system, improve transmission efficiency, and reduce transmission noise.
③ The vehicle's structure is simplified; traditional clutches, gearboxes, and drive shafts will no longer exist. This also means saving more space.
④ It reduces the performance requirements for electric vehicle motors and features high redundancy and reliability.
The disadvantages are also obvious.
① To ensure coordinated movement of all wheels, high requirements are placed on the synchronous and coordinated control of multiple motors.
② The distributed installation of electric motors presents many technical challenges, including structural layout, thermal management, electromagnetic compatibility, and vibration control.
③ Increasing the unsprung mass and the moment of inertia of the wheel hub will affect the vehicle's handling.
④ Afraid of losing
